Pictor A (PKS 0518-45): From Nucleus to Lobes

Abstract

We present a variety of new imaging and kinematic data for the double-lobed radio galaxy Pictor A. The new optical data include Hubble Space Telescope (HST) continuum and [O III], emission-line images (at a resolution of 25-100 mas) and ground-based imaging and spectroscopy (at a resolution of ~1.5"). The ground-based images show Hα filaments and loops which extend to the north and west of the optical core. The radio continuum data include 3 cm Australia Telescope images of the core, at a resolution comparable to that of the optical, ground-based images, and a VLBI image of a jet in the compact core (at a resolution of 2-25 mas), which seems to align with a continuum ``jet'' found in the HST images. The core radio jet, the HST optical continuum ``jet,'' and the NW Hα filaments all appear to be aligned with the extended, low-luminosity radio continuum bridge which Perley et al. have traced out to the optical-synchrotron hot spot in the NW lobe of this object. The Hα filaments which appear to lie in the path of this trajectory are associated with a disrupted velocity field in the extended ionized gas. These filaments (as well as the extended [O III] emission found at mas scales in the HST images) may have been pushed to the north, out of the path of the jet. The ground-based spectra which cover this trajectory also yield line ratios for the ionized gas which have anomalously low [N II] (6564), suggesting either a complex, clumpy structure in the gas with a higher cloud-covering factor at larger radii and with denser clouds than is found in the nuclear regions of most NLRG and Seyfert 2 galaxies, or some other, unmodeled, mechanism for the emergent spectrum from this region. The Hα emission-line filaments to the north appear to be associated with a 3 cm radio continuum knot which lies in a gap in the filaments ~4" from the nucleus. Altogether, the data in this paper provide good circumstantial evidence for nondisruptive redirection of a radio jet by interstellar gas clouds in the host galaxy.